Subtropical Storm Deni (Potential Scenario)
Subtropical Storm Deni was a rare, very short-lived subtropical cyclone in the South Atlantic basin. Deni was the first tropical storm-strength subtropical or tropical cyclone since Subtropical Storm Cari of March 2015. Deni was only the fourth named storm since the Brazilian Navy Hydrographic Center started naming South Atlantic subtropical and tropical cyclones in 2011, demonstrating the rarity of storms in the basin. Deni had no impacts and only caused 1 fatality. Meteorological History About 2 weeks prior to initial formation, models were in good agreement that a weak to moderate subtropical or tropical cyclone would develop in the South Atlantic, a rare occasion due to highly unfavorable conditions usually in place over the basin, with persistent large amounts of wind shear. Models remained strangely consistent, and approximately 4 days prior to Deni's formation, an extratropical cyclone branched north as it continued to move eastward. As the branch of the main extratropical cyclone exited off the coast of South America, a separate low pressure developed on August 10. This low pressure continued to move steadily eastward as the branch of the extratropical cyclone began to retreat back south. Development was inhibited due to the low pressure being connected to a frontal system. The system, still connected to front, gradually organized throughout the day on August 11, and it was noted that the system was becoming increasingly detached from the main system. Having already attained tropical storm-force winds, at 1200 UTC on August 12, the Brazilian Navy Hydrographic Center announced that the system had entirely detached itself from the frontal system and had become a subtropical storm and was assigned the name Deni. Due to unfavorable conditions in the storm's path, Deni was forecast to see little to no intensification before its predicted dissipation within the next 24 hours. The storm peaked on the same day of its formation as a weak subtropical storm, with maximum sustained winds of 40 mph and a minimum pressure of 1008 mbars. A fisherman was reported missing on the evening of August 12 after heading out to fish and steering his boat into Deni, where it is believed to have been overturned due to poor quality of construction. The man was later presumed dead, and the death was attributed to the storm. At 0400 UTC on August 13, the Brazilian Navy Hydrographic Center stated that Deni was beginning to become less organized, and was expected to rapidly dissipate in 6 to 12 hours. The prediction was correct, and at 1800 UTC the Brazilian Navy announced the dissipation of Deni, and that it had been absorbed by the same frontal system from which it originated, having never become a tropical cyclone. Preparations and impact Deni was never expected to impact land, so preparations were relatively light. However, the Government of Brazil advised all beachgoers to be careful and be on guard for possible rip currents for beaches from Rio De Janeiro south to the Brazil-Uruguay border. Ships heading southward from Brazil or northward from Argentina were held in their respective ports to avoid potential issues that could have been encountered in Deni. The missing fisherman who was later presumed dead was reported to have been from a rural area in extreme southern Brazil, and was not known to port authorities. Prior to moving over the South Atlantic, the precursor of Deni brought light rains to central South America. Aftermath In all, Deni caused no damage and 1 fatality. Rip currents were sporadic, and all ship traffic resumed on August 14. Unusualness and Records Deni was a rare South Atlantic tropical cyclone, becoming only the seventh confirmed tropical storm-strength subtropical or tropical cyclone in the basin since record-keeping began in 1991. Upon dissipation, Deni became the fourth named storm in a row to not achieve fully tropical characteristics, following Arani in 2011, Bapo and Cari, in February and March 2015, respectively. Tropical cyclones are very rare in the South Atlantic due the short lived nature of the storms and unfavorable conditions preventing tropical transition. There has only been one hurricane strength tropical cyclone in the South Atlantic, which was Hurricane Catarina back in 2004, which is considered as an unprecedented event. Deni became the first storm on record in the South Atlantic in the month of August, which is considered as winter in the Southern Hemisphere. August in the Northern Hemisphere is equivalent to February in the Southern Hemisphere. Finally, Deni also became the fourth subtropical or tropical cyclone in 2016 to develop outside of the usual seasonal bounds (the South Atlantic has no official bounds, but most storms develop between November and April). Prior to Deni, Hurricane Pali developed in January in the East Pacific, followed by Hurricane Alex in the same month in the Atlantic. Then, a few months later, Tropical Storm Abela developed in July (equivalent to January in the Northern Hemisphere) in the South-West Indian Ocean. Category:South Atlantic tropical cyclone Category:Cyclones Category:Subtropical storm Category:Money Hurricane Category:Potential Scenario Series/South Atlantic